1. Field of the Invention
The invention relates to a method for producing a single crystal composed of silicon from molten granules. The method comprises producing a first volume of molten silicon between a growing single crystal and the lower end of a conical tube composed of silicon, the tube being closed off at the lower end and enclosing a central opening of a rotating plate composed of silicon, below which the tube extends, by means of a first induction heating coil, which is arranged below the plate;
producing a second volume of molten silicon with the aid of a second induction heating coil, which is arranged above the plate;
melting the lower end of the tube to an extent such that a passage opening for the second volume of molten silicon is produced; and
crystallizing monocrystalline silicon on the growing single crystal with consumption of molten silicon from the first and the second volume.
2. Background Art
The method and devices suitable for carrying it out are described in DE 102 04 178 A1. DE 10 2008 013 326 A1 describes an induction heating coil which can be used as the second induction heating coil of the method. It has projecting segments in the center of the lower side, with the aid of which segments the film of molten silicon that flows through the conical tube can be heated and kept liquid. When carrying out the method, it is possible for disturbing events to occur which reduce the yield of single crystals from which monocrystalline semiconductor wafers can be fabricated. Thus, dislocations can suddenly form or molten silicon flows away at the side of the single crystal that has grown up to that point.
These methods differ from the floating zone method (FZ method) essentially by the fact that granules are melted instead of a polycrystalline block in order to provide the predominant portion of the molten silicon required for growing the single crystal and by virtue of the fact that a dedicated induction heating coil (“inductor coil”) is respectively used for melting the granules and for controlling the crystallization of the single crystal.